1. Field of the Invention
Embodiments of the present invention relate to a silicon carbide semiconductor device and a method of manufacturing a silicon carbide semiconductor device.
2. Description of the Related Art
As is widely known, semiconductor elements using silicon carbide (SiC) as a material are expected to replace those of silicon (Si) in next generation semiconductor devices. The reason for this is that compared to conventional semiconductor elements using Si as a material, SiC has various advantages such as use in environments of high temperatures (200 degrees C. or more) and being able to reduce the on-resistance of an element to 1 few-hundredths of that of a conventional semiconductor element. Such advantages are enabled by characteristics of the material itself such as the bandgap of SiC being about 3 times that of Si and the dielectric breakdown field strength being nearly 10 times that of Si.
Schottky diodes and planar vertical metal oxide semiconductor field effect transistors (MOSFET) have become commercial SiC semiconductor devices.
Nonetheless, for the most part, SiC MOSFETs have low channel mobility and therefore, have high channel resistance and cannot obtain the expected low on-resistance. One contributing factor is that since SiC has a small impurity diffusion coefficient, a channel region is inevitably created by ion implantation and, crystal defects induced by ion implantation and interstitial impurities that are not activated lower channel mobility.
On the other hand, SiC MOSFETs having a channel region created by epitaxial growth (hereinafter, abbreviated as “epi-growth”) are known (for example, refer to International Publication No. 2004/036655). In such devices, a low-concentration p−-type epitaxial layer is grown as a channel region whereby high channel mobility is realized by high crystallinity and a suppression of impurity diffusion. Further, breakdown voltage between the drain and the source consequent to making the p−-type epitaxial layer of a low concentration is maintained by providing a high-concentration p-type ion implanted layer under the p−-type epitaxial layer.